I just posted a thread about this. It's my video you referenced in the OP, again given below (see 2:17):
[youtube]http://www.youtube.com/watch?v=RlW5_H-SCig[/youtube]
... And here's a flight I did the next day. The wind actually much heavier and more sustained this day, but I was not flying full throttle as often as in the prior videos. It seems jello was reduced, don't see much of it, just a bit:
[youtube]http://www.youtube.com/watch?v=Kb74K3wqRPE[/youtube]
I'll update after more flights and fiddling around.
Prop balance? Maybe.
More rigid dampeners needed? Maybe.